1. Field of the Invention
The present invention relates generally to analysis of X-ray images, and more particularly, to the automatic detection of vertebra endplates for measuring deformities of pathological spines in digital radiography.
2. Description of Related Art
In a previously disclosed invention, “Detection of vertebra endplates in digital radiography”, U.S. application Ser. No. 09/638,123 an evidence reasoning approach is proposed. First, local pieces of evidence of different kinds are collected. They are then combined by a rule-based deduction to incorporate certain geometric constraints about endplate shape to determine the positions of endplates. Because the reasoning about endplate positions in the previously disclosed technique is mainly local, it is difficult to apply some global shape constraints. Global constraints are especially useful when there are other organs interfering with the endplate, causing part of the endplate image to be blurred, obscured, or underexposed. Errors in local reasoning also tend to propagate: if a mistake is made at one place, it will affect the decision making at other places.
In this invention, a global reasoning approach is adopted. Decision-making about endplate positions at local regions is deferred until information is gathered about all endplates in the image. This is achieved via a dynamic programming approach. Dynamic programming is a general method for optimization. The invention formulates the endplate detection problem in a form suitable to solve by dynamic programming. Besides, the conventional dynamic programming approach is generalized to allow global constraints to be enforced in a progressive manner. This is realized by introducing backward tracing during forward computation of endplate scores. As a global constraint on vertebra shape, an analytic model about vertebra height distribution is proposed.